1. Field of the Invention
The present invention relates to an information recording and retrieval method for optically recording and retrieving information in recording media, and also relates to an information recording and retrieval apparatus.
2. Description of the Related Art
Optical disks have the following prominent features. Semiconductor lasers can be used as a light source. Recording media (disks) can be removed from the recording and retrieval apparatus. Optical disks cost lower per bit of the recording media. Accordingly, a desirable optical disk apparatus is a higher-density, higher-speed one that still has the above-mentioned features. Conventionally, an optical disk has a single recording layer, but, to record a larger-volume data, double-layer, triple-layer optical disks have been developed. The number of recording layers has reached eight for a read-only type multiple-layer optical disk. As other types of multiple-layer recording media, a data-recordable type optical disk is disclosed. In this type of optical disk, a plurality of data-recording layers and a single servo layer are combined, and light sources are provided respectively for recording data purpose and for servo purpose. The light beams eradiated from the light source for servo form a minute beam spot on the servo layer, and always following the track formed in the surface of servo layer. The light beams eradiated from the light source for data recording maintain a constant geometrical arrangement relationship with the beam spot formed in the servo layer, and thus data is recorded in a plurality of recording layers. The retrieval of data from each of the layers is carried out by moving the spot for retrieving data in the vertical direction of the disk, and by detecting the signal in the data layer while the cross-talk from other layers is reduced by use of a pinhole (U.S. Pat. No. 6,540,397).